This invention relates to a method of providing reinstatement sheathing to cover the exposed glass in the neighbourhood of a splice formed to butt join the ends of two plastics sheathed glass optical fibres.
Optical fibre is conventionally made by a batch process, and hence in the manufacture of long lengths of cable the or each optical fibre is liable to be composed of a number of shorter lengths of optical fibre joined end to end in a permanent manner. Such permanent points are referred to as splices, and the conventional form of such a splice is a fusion splice.
The initial strength of freshly drawn glass fibre is much reduced if it becomes scratched. Such scratching is very liable to occur if it is allowed to come into contact with almost any solid surface, and therefore it is conventional practice to coat such fibres with plastics protective sheathing immediately after they are drawn and before they come into contact with anything else.
To make a fusion splice, the protective plastics sheathing is stripped back a short distance from the end of each fibre to expose bare glass (silica) fibre. Each fibre end is provided by cleaving with a plane face normal to the fibre axis. The fibres are aligned, butted together, and then slightly separated for the striking of an arc between them. The ends are then advanced into the arc where they fuse together. In making such a splice it is necessary for the bare fibre to protrude from its plastics protective sheathing for a short distance so that no plastics material comes within the range of the arc where it would be liable to introduce contamination. Therefore, there is a gap in the protective sheathing extending a short distance on either side of the splice. It is necessary to fill this gap with reinstatement sheathing without letting the bare fibre become scratched.
One known method of providing reinstatement sheathing involves placing the splice in a U-shaped trough that is rather longer than the gap in the sheathing and just fits around the plastics sheathing. In this way a mould is formed whose sides are formed by the trough and whose ends are formed by the original plastics sheathing. Liquid resin is poured into this mould and cured. The drawback of this approach is that the resulting reinstatement sheathing, after withdrawal from the mould, does not have the same circularly symmetric profile as the original sheathing, but has a `flat` terminating at each long side in a meniscus. This change of profile can introduce snagging problems when the plastics protected fibre is being cabled.